class_docstr: Defines a dataset composed of Examples along with its Fields.
  
  Attributes:
      sort_key (callable): A key to use for sorting dataset examples for batching
          together examples with similar lengths to minimize padding.
      examples (list(Example)): The examples in this dataset.
      fields (dict[str, Field]): Contains the name of each column or field, together
          with the corresponding Field object. Two fields with the same Field object
          will have a shared vocabulary.
docstr: Remove unknown words from dataset examples with respect to given field.
  
  Arguments:
      field_names (list(str)): Within example only the parts with field names in
          field_names will have their unknown words deleted.
docstr_tok: ["Remove","unknown","words","from","dataset","examples","with","respect","to","given","field",".","Arguments",":","field_names","(","list","(","str",")",")",":","Within","example","only","the","parts","with","field","names","in","field_names","will","have","their","unknown","words","deleted","."]
code: def filter_examples(self, field_names):
      """Remove unknown words from dataset examples with respect to given field.
  
      Arguments:
          field_names (list(str)): Within example only the parts with field names in
              field_names will have their unknown words deleted.
      """
      for i, example in enumerate(self.examples):
          for field_name in field_names:
              vocab = set(self.fields[field_name].vocab.stoi)
              text = getattr(example, field_name)
              example_part = [word for word in text if word in vocab]
              setattr(example, field_name, example_part)
          self.examples[i] = example
  
imports: import csv
  import gzip
  import io
  import os
  import shutil
  import tarfile
  import zipfile
  from functools import partial
  import torch.utils.data
  from torchtext.data.utils import RandomShuffler
  from torchtext.utils import download_from_url
  from .example import Example
label_desc: Use image node_id 9 for calling the Dataset obj's underlying member method code with example usage: obj.filter_examples(field_names) without return types